This invention relates to downhole apparatus. In particular, but not exclusively, the invention relates to drilling apparatus and a drilling method, and to a flow pulsing method and a flow pulsing apparatus for a drill string.
In the oil and gas exploration and extraction industries it is well known that providing a percussive or hammer effect tends to increase the drilling rate that is achievable when drilling bores through hard rock. In such drilling operations drilling fluid or xe2x80x9cmudxe2x80x9d is pumped from the surface through the drill string to exit from nozzles provided on the drill bit. The flow of fluid from the nozzles assists in dislodging and clearing material from the cutting face and serves to carry the dislodged material through the drilled bore to the surface. It has been recognised that providing a pulsing fluid flow from the nozzles may also serve to increase the drilling rate.
Apparatus utilising one or both of these principles is described in U.S. Pat. No. 2,743,083 to Zublin, U.S. Pat. No. 2,780,4438 to Bielstein, and U.S. Pat. Nos. 4,819,745, 4,830,122, 4,979,577, 5,009,272 and 5,190,114 all to Walter. A pulsing fluid flow is achieved by restricting the drilling fluid flow area through the apparatus, the restriction creating a pressure force which provides the percussive effect. The flow restriction may be achieved by a variety of means, including valves which rotate about the longitudinal axis of the string, valves which rotate about a transverse axis, axially reciprocating valves and flap valves. The valves members are driven or reciprocated using drilling fluid driven turbines of various forms, or fluid pressure forces created by the movement of the valve member in the flow of drilling fluid.
It is among the objectives of the present invention to provide an improved flow pulsing method and apparatus for a drill string.
In accordance with one aspect of the present invention there is provided flow pulsing apparatus for a drill string, the apparatus comprising:
a housing for location in a drill string above a drill bit, the housing defining a throughbore to permit passage of drilling fluid therethrough;
a valve located in the bore and including first and second valve members each defining a respective axial flow opening and which openings are aligned to collectively define an open axial drilling fluid flow port through the valve, the first member being rotatable about a longitudinal axis of the housing to vary the alignment of the openings and thus vary the open area of said port to, in use, provide a varying flow therethrough and variation of the drilling fluid pressure; and
drive means operatively associated with the valve for rotating the first member.
According to another aspect of the present invention there is provided a flow pulsing drilling method comprising the steps:
providing a valve in a drill string bore including first and second valve members each defining a respective axial flow opening and which openings collectively define an open axial flow port through the valve; and
rotating the first member about a longitudinal axis to vary the alignment of the openings such that the open area of said axial flow port varies with said rotation to provide variable flow therethrough and thus produce varying fluid pressure in the drilling fluid.
The provision of an open axial flow port minimises the possibility of the port becoming blocked by large particles or debris carried by the drilling fluid into the housing. Further, the use of first and second valve members which rotate relative to one another facilitates clearing of the port if any particles or debris should become lodged in the valve.
The apparatus may form part of a rotary drilling string, that is a string that is rotated from surface, or may be incorporated in a downhole drilling motor and use the rotary drive of the motor to rotate the first valve member.
Preferably also, the valve openings are of similar shape such that when the openings are aligned the maximum flow area of the axial flow port corresponds to the area of each opening: the axis of rotation of the first valve member may be offset from the second member such that rotation of the first member moves the openings out of alignment; or the axes of non-circular openings may coincide. In the preferred embodiment the valve openings are in the form of transverse slots on a common axis.
Preferably also, the drive means is driven by passage of drilling fluid therethrough. Most preferably, the drive means is in the form a positive displacement motor.
Preferably also, the apparatus includes a pressure responsive device which will expand or retract in response to the varying drilling fluid pressure created by operation of the apparatus; this expansion or retraction provides the desired percussive effect at the drill bit. The device, which may be in the form of a shock sub or tool, may be provided above or below the valve. Alternatively, the valve may form part of such a device.
In accordance with another aspect of the present invention there is provided downhole flow pulsing apparatus, the apparatus comprising:
a housing for location in a string, the housing defining a throughbore to permit passage of fluid therethrough;
a valve located in the bore defining a flow passage and including a valve member, the valve member being movable to vary the area of the flow passage to, in use, provide a varying fluid flow therethrough; and
a fluid actuated positive displacement motor operatively associated with the valve for driving the valve member.
The use of a positive displacement motor provides for alignment; or the axes of non-circular openings may coincide. In the preferred embodiment the valve openings are in the form of transverse slots on a common axis.
Preferably also, the drive means is driven by passage of drilling fluid therethrough. Most preferably, the drive means is in the form a positive displacement motor.
Preferably also, the apparatus includes a pressure responsive device which will expand or retract in response to the varying drilling fluid pressure created by operation of the apparatus; this expansion or retraction provides the desired percussive effect at the drill bit. The device, which may be in the form of a shock sub or tool, may be provided above or below the valve. Alternatively, the valve may form part of such a device.
In accordance with another aspect of the present invention there is provided downhole flow pulsing apparatus, the apparatus comprising:
a housing for location in a string, the housing defining a throughbore to permit passage of fluid therethrough;
a valve located in the bore defining a flow passage and including a valve member, the valve member being movable to vary the area of the flow passage to, in use, provide a varying fluid flow therethrough; and
a fluid actuated positive displacement motor operatively associated with the valve for driving the valve member.
The use of a positive displacement motor provides for close control of the rate at which the drive member is driven; typically, the speed of the motor is directly proportional to the rate of flow of fluid through the motor. Thus, the frequency of the changes in fluid flow may be subject to the same close control.
Preferably, the positive displacement drive motor includes a rotor and the rotor is linked to the valve member. Most preferably, the rotor is utilised to rotate the valve member. The rotor may be linked to the valve member via a universal joint which accommodates any transverse movement of the rotor. Alternatively, the rotor is linked to the valve member and communicate its transverse movement to the valve member. In this situation, the valve member may cooperate with a second valve member, each valve member defining a flow port, the alignment of the flow ports varying with the transverse movement of the first valve member.
Preferably also, the positive displacement motor operates using the Moineau principle. Such motors include a lobed rotor which rotates within a lobed stator, the stator having one more rotor than the rotor. The preferred embodiment of the present invention includes a 1:2 Moineau motor, that is the rotor has one lobe and the stator has two lobes.